Mechanisms of Sex in Escherichia coli

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The discovery of the gene transfer mechanisms could be attributed by the work of Lederberg and Tatum back in 1946. Using Escherichia coli(E.coli) as their model, they proposed the genetic materia of E.coli could be exhanged via sexual process. In order to prove their hypothesis, they mutated 2 wild type E.coli strains(K12) using X-ray or ultra-violet radiation to produce Y-10 and Y-24 mutant strains. The former was auxotrophic to threonine, leucine and thiamin whereas the latter failed to produce biotin, phenylalanine and cystine[1]. These mutant could only survive in mininal media plates provided that the aforementioned amino acids are supplied accordingly to each mutant strains.

Further experimentation was conducted where they mixed
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transformation and conjugation. The former would imply the presence of unknown transforming factors which brought about gene mutations that caused the reversion of mutant E.coli strain to wild type strain. The latter would then suggest that random gene reassortment in new combinations which required the fusion of bacterial cells in order to exchange genetic substances. Regrettably, no further evidences were produced to substantiate either one of these models.

In the BIOL2202 bacteria genetics practical, our results can hardly discriminate which sex mechanism was employed by E.coli to revert back to prototroph as the donor(JC158) and recipient strands(AB1157) were added into a Erlenmeyer flask and mixed together to facilitate conjugation. Besides, the reversion could also be attributed to transformation due to unknown transforming factors which somehow mutated the gene back to wild type configuration. When mixing began, both transformation and cell conjugation were possible, thus it was hard to differentiate which mechanism that ultimately leads to the appearance of prototroph.

Given that there were two plausible models, Bernard Davis was able to prove that conjugation was the underlying mechanism for the unsolved mystery via his U-tube experiment conducted in 1950. His U-tube was designed with a separation which composed of ultrafine fritted glass disc in the middle that would only allow